Diatoms are key indicators of marine environmental health. To further understand how diatoms respond to varying degrees of salinity, either due to climate change or brine waste discharge into marine environments, two different diatom species were studied. Thalassiosira pseudonana and Chaetoceros muelleri were cultured at three different salinities namely, 26 practical salinity units (PSU or parts per thousand), 36 PSU (standard salinity for culturing of seawater species) and 46 PSU. Changes in silica and organic content within the cultured diatoms were analysed using solid-state (29)Si{(1)H} cross-polarization-magic angle spinning (CP-MAS) nuclear magnetic resonance (NMR) and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopies coupled with analysis of variance. (29)Si CP-MAS NMR showed that qualitatively the Q4:Q3 area ratios of C. muelleri, grown away from standard salinities, increased in response to the formation of more condensed (2 ≡SiOH → ≡Si-O-Si≡ + H2O) and/or an increase in closely associated organic matter to the Q4 component of the diatoms. This was not observed for T. pseudonana. However, both species showed the appearance of a new peak centered at 1575-1580 cm(-1) in the ATR-FTIR spectra, designated as the C═N band of nitrogenous purine-type compounds. Further, the C. muelleri species was shown to produce more extracellular polymeric substances at non-standard salinities. On this basis, results suggest that there is a strong relationship between diatom composition and salinity and that C. muelleri is more sensitive to its environment than T. pseudonana.

A. ferrooxidans and their metabolic products have previously been explored as a viable alternative depressant of pyrite for froth flotation; however, the mechanism by which separation is achieved is not completely understood. Scanning electron microscopy (SEM), photoemission electron microscopy (PEEM), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and captive bubble contact angle measurements have been used to examine the surface physicochemical properties of pyrite upon exposure to A. ferrooxidans grown in HH medium at pH 1.8. C K-edge near edge X-ray absorption fine structure (NEXAFS) spectra collected from PEEM images indicate hydrophilic lipids, fatty acids and biopolymers are formed at the mineral surface during early exposure. After 168 h, the spectra indicate a shift towards protein and DNA, corresponding to an increase in cell population and biofilm formation on the surface, as observed by SEM. The Fe Ledge NEXAFS show gradual oxidation of the mineral surface from Fe(II) sulfide to Fe(III) oxyhydroxides. The oxidation of the iron species at the pyrite surface is accelerated in the presence of A. ferrooxidans and extracellular polymeric substances (EPS) as compared to HH medium controls. The surface chemical changes induced by the interaction with A. ferrooxidans show a significant decrease in surface hydrophobicity within the first 2 h of exposure. The implications of these findings are the potential use of EPS produced during early attachment of A. ferrooxidans, as a depressant for bioflotation.

No abstract